A dynamic 2d char array - arrays

Question

I have a question about the C code for a dynamic 2d char array: malloc buffer overflow. The program idea is to initialize a global 2d char array, when the program is running, type some words, and save them into that 2d char array. I'm not familiar with the realloc function. What is wrong here?
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
char **array_history;
int count = 0;
#define MAX_LINE_CHARS 1024
int main (void){
array_history = malloc(sizeof(char *));
while (1) {
char line[MAX_LINE_CHARS];
if (fgets(line, MAX_LINE_CHARS, stdin) == NULL)
break;
array_history = realloc(array_history, sizeof(char*)*(count + 1));
int len_size = strlen(line) + 1;
array_history[count] = malloc(len_size*sizeof(char));
for (int i = 0; line[i] != '\0'; i++) {
array_history[count][i] = line[i];
// printf("%c", line[i]);
}
// printf("%s", array_history[0]);
// for (int i = 0; history[i] != NULL; i++) {
// printf("%s\n", history[i]);
// }
count++;
}
for (int i = 0; array_history[i] != NULL; i++) {
printf("%s", array_history[i]);
}
return 0;
}

Answer 1

You have some errors in your code.
You fail to terminate your strings and you fail to add the sentinel value that you are using when printing your string.
A fixed version could look like this:
(You should add more error checking for malloc etc.)
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#define MAX_LINE_CHARS 1024
int main (void){
char **array_history;
int count = 0;
array_history = malloc(sizeof(char *)*(count+1));
// TODO: Check for NULL
array_history[0] = NULL; // Terminate the array.
while (1) {
char line[MAX_LINE_CHARS];
if (fgets(line, MAX_LINE_CHARS, stdin) == NULL)
break;
void *temp_ptr = realloc(array_history, sizeof(char*)*(count + 2));
// TODO: Check for NULL
array_history = temp_ptr;
int len_size = strlen(line) + 1;
array_history[count] = malloc(len_size*sizeof(char));
array_history[count + 1] = NULL; // Add sentinel for your array
int i;
for (i = 0; line[i] != '\0'; i++) {
array_history[count][i] = line[i];
// printf("%c", line[i]);
}
array_history[count][i]=0; // Terminate the new string.
// Or simply use strcpy(array_history[count],line);
// printf("%s", array_history[0]);
// for (int i = 0; history[i] != NULL; i++) {
// printf("%s\n", history[i]);
// }
count++;
}
// Instead of terminating NULL value you could just use condition `i<count`
for (int i = 0; array_history[i] != NULL; i++) {
printf("%s", array_history[i]);
}
return 0;
}